It was the most startling of warnings. If the US does not get its finances in order “we will have a European situation on our hands, and possibly worse”, claimed Paul Ryan, the new Republican chairman of the House of Representatives budget committee.

The consequences of not tackling the country’s mounting debt burden would be dire, he last week told an audience of leading budget experts and economists at a gathering in Washington. “We will have the riots in the streets, we will have the defaults, we will have all of those ugliness problems,” he said, referring to “French kids lobbing Molotov cocktails at cars, burning down schools because the retirement age will be moved from 60 to 62”.

As it stands today, the US borrows about 40 cents of every dollar it spends. Curbing the budget deficit has been the stated mission of Mr Ryan, a rising Republican star, for several years. But such calls for action have multiplied in Washington in recent months, igniting what some say is the fiercest debate over fiscal and budgetary policy in decades.